The present invention concerns an electronic apparatus which can be worn on the wrist, particularly a diver's wristwatch, a bathymeter or an altimeter, including a case and a pressure sensor, which is mounted in a housing of the case and has a surface exposed to the inside of the housing for receiving the ambient pressure, said housing opening out on to an external face of the case and being closed on said face by a cap having an external wall provided with at least one orifice in front of the housing for transmitting the ambient pressure from outside the case to the housing.
A wristwatch of this type is known, disclosed in EP Patent No. 195 636, wherein the housing of the pressure sensor is provided in a lateral projection of the case and opens onto the upper face of the case, such that the sensor can be set in place from the top. According to one construction, which is currently the most common, the pressure sensor includes a piezo-resistive element made of silicon which is housed in a pot-shaped structure and encased in a silicon gel to protect it from the effects of water. This gel is also coated with a flexible layer of silicon resin or rubber, which forms the exposed surface of the sensor and which transmits the ambient pressure to the piezo-resistive element. Above, the cap closing the recess is formed by a perforated circular plate. The orifices of the plate are arranged along its periphery, so as not to be opposite the silicon element and the gel encasing the latter. The object of this arrangement is to prevent foreign bodies engaging in these orifices from being able to damage the silicon element or gel.
However, such an arrangement has two drawbacks. On the one hand, it means that the closing plate has to be enlarged so that the orifices are outside the central region occupied by the sensor. On the other hand, it would be desirable to avoid the silicon element having prolonged exposure to solar light, but the construction described hereinbefore does not sufficiently stop diffusion of light in the sensor.
EP Patent No. 677 798 discloses a wristwatch of the type indicated in the introduction hereinbefore, but in which a pipe placed in a cavity at the back of the watchcase forms the housing for the pressure sensor. In order to prevent the pressing of the case against the wearer's wrist interfering with transmission of the ambient pressure to the sensor, the back of the case includes grooves, whereas the housing is covered by a cover or lid having, on the outside, a support surface flush with the back of the case, for pressing against the wearer's wrist and leaving communication between the grooves and the sensor housing behind the cover or through its lateral openings. Such a construction has the drawback of leading to great thickness of the watch. On the other hand, it is not arranged to prevent solar light reaching the sensor, particularly when the watch is not on the wrist.